Premature Mortality in the United States: Public Health
Issues in the Use of Years of Potential Life Lost

INTRODUCTION

Mortality statistics are frequently used to quantitate the
extent of public health problems and to determine the relative
importance of the various causes of death. Analyses of crude and
age-adjusted death rates have traditionally played an important
role in this process; they enable priorities to be set and
progress towards the achievement of public health goals to be
monitored. Although these rates are important measures of the
nation's health status, they often fail to tell the entire story
of temporal changes in mortality. Since most deaths occur among
persons in older age groups, crude and age-adjusted mortality
data are dominated by the underlying disease processes of the
elderly.

Alternative measures have been proposed to reflect the
mortality trends of younger age groups. These measures provide a
more accurate picture of premature mortality by weighting deaths
occurring at younger ages more heavily than those occurring in
older populations. One of these measures is the years of
potential life lost (YPLL).
HISTORICAL PERSPECTIVES ON PREMATURE MORTALITY

In 1947, as a supplement to crude mortality figures, Dempsey
introduced a method of quantifying premature mortality to measure
the changing mortality consequences of tuberculosis (1). She
tabulated the "potential years of life lost" by subtracting the
age at death from the life expectancy at birth for persons who
died during 1942 from heart disease, cancer, and tuberculosis.
Greville subsequently altered this calculation, weighting each
death by the life expectancy remaining at death (2). He also
introduced the use of life tables calculated on the assumption
that the given disease had been eliminated as a cause of death
for all older age groups. This adjustment (the "zero-mortality
assumption") only slightly changed the overall distribution of
years of life lost and did not affect the rank order of causes
(3).

Haenszel proposed directly age adjusting death rates to a
standard population and then computing years of life lost from
the resulting standardized deaths (4). Studies comparing
temporal trends of premature mortality in populations widely
separated in time have used a similar approach (5,6). In
addition, standardized rates of "potentially productive years of
life lost" have been developed to adjust for different age
structures among populations and to describe race- and
sex-specific patterns of premature mortality (7).

The use of premature mortality measures has recently become
somewhat more common as a mechanism for establishing public
health priorities (7-10). For this reason, the CDC introduced
Table V of the MMWR in 1982. This table appears monthly and
ranks the leading causes of premature mortality (11).
METHODOLOGIC ALTERNATIVES IN YPLL CALCULATION

Although many authors have emphasized the importance of the
concept of premature mortality, there is no consensus on a
functional definition or the best means of deriving a
quantitative measure. Such a measure is necessary to monitor
yearly trends in the pattern of premature mortality as well as to
compare the relative importance of specified causes of death.
This report will focus on YPLL, the measure of premature
mortality used at CDC for the preparation of Table V of the MMWR.
This section documents the current method of calculating YPLL
used at CDC and discusses several adaptations of this measure for
use in different situations.
Present Method of Calculation

For routine publication of Table V, YPLL is defined as the
number of years of potential life lost by each death occurring
before a predetermined end point, set at age 65 years. CDC
calculates YPLL over the age range from birth to 65 years using
age-specific death rates for 15 selected causes and supplementary
data on causes of infant mortality, provided yearly by the
National Center for Health Statistics (NCHS) (12). For
timeliness, these data are estimated from a 10% sample of all
death certificates filed during the year. Causes of death are
grouped by an algorithm devised by NCHS to reflect the underlying
cause of death as reported on the death certificate and the
pathophysiologic process or organ system involved (i.e.,
malignant neoplasms or diseases of the heart).

The cause- and age-specific death rate is multiplied by the
estimated population in that age range (provided by the Bureau of
the Census) to determine the number and age distribution of
deaths attributable to a specific cause (13). The number of
deaths for each age is then multiplied by the years of life lost
(the difference between the designated 65-year end point and the
midpoint of the age range) to give an age-specific YPLL. For
example, in the population 15-24 years old, the midpoint is 20
years and the YPLL is 45 years. Finally, the age-specific YPLLs
are summed to give a total YPLL for each cause. The resulting
distribution of YPLL, by cause, appears monthly as Table V (Table
1).

A persistent controversy in the calculation of YPLL concerns
the definition of an upper end point. The CDC method of
calculation does not count deaths of persons 65 years or older
and assumes only 5 years of life lost for deaths of persons aged
55-64 years. In 1984, however, the remaining life expectancy for
a 60-year-old person was 20.4 years (12). Thus, deaths in older
age groups are underrepresented by the upper age limit of 65
years. However, this method preserves the emphasis on causes of
mortality among younger persons.
Life-Expectancy Method

An alternative form of YPLL can be calculated that emphasizes
the total life expectancy remaining at the time of death (Table
2). Age-specific death rates and population estimates are
obtained from the same sources, but would not be truncated at age
65 (12,13). The number of deaths is estimated as above, but the
YPLL for each death is calculated by taking the difference
between the midpoint of the age range and the remaining life
expectancy at that age from an abridged life table published
yearly by NCHS (12). This table assumes that the risk of death
in future years is approximated by the age-specific death rates
for all causes in effect for the past year. For example, in the
75- to 84-year age group, the remaining life expectancy at the
midpoint (80 years) was 8.2 years in 1984.

The number of deaths in each age group, grouped by underlying
cause of death, is then multiplied by the remaining life
expectancy at the midpoint of each age range, and the resulting
numbers for all age groups are summed to obtain the total YPLL
for this cause. Not surprisingly, this substantially changes
both the total YPLL and the relative rankings for each cause
(Table 3). When derived by the remaining-life-expectancy method,
the proportion of YPLL attributable to each individual cause more
closely resembles the pattern of cause-specific mortality than
that of YPLL before age 65 (Figure 1).
Mortality Groups

Another issue in the calculation of YPLL concerns the grouping
of underlying causes of death as provided by NCHS. As a measure
of mortality, YPLL underestimates the importance of diseases that
contribute to, but are not recorded as, the underlying cause of
death. A complete listing of any condition contributing to death
is available from the NCHS tape "Mortality--Multiple Causes of
Death," on which each condition recorded on the death certificate
as either a contributing or an underlying cause of death is coded
according to the International Classification of Diseases, Ninth
Revision, Clinical Modification (ICD-9 CM).

In addition, it is impossible at present to calculate YPLL on a
timely basis for those diseases or disease categories that are
not reported separately by NCHS, such as a composite category of
YPLL attributable to all infectious diseases. Age-specific death
rates are supplied annually by NCHS for only the 15 leading
causes of mortality and certain causes of infant mortality. For
example, no summary data on mortality due to infectious diseases
would be available in the annual report other than the categories
of pneumonia and influenza or septicemia (12). However, the tape
"Mortality--Underlying Cause of Death" contains detailed listings
of all deaths, with the coded underlying cause of death. This
tape is available from NCHS, but only after a lag time of several
years after publication of data from the 10% sample. Therefore,
although these data allow for a more individualized design of
mortality groups by ICD-9 CM codes, they are not useful when
timeliness is important.
Age Limits

Some research may benefit from alterations in the YPLL age
limits, either to emphasize the effects of a condition in a
population at increased risk of illness or to study a particular
subpopulation of interest. For example, a recent review of the
premature mortality consequences of the acquired immunodeficiency
syndrome (AIDS) was limited to persons aged 25-44, the ages with
the highest incidence of illness (14). The most common use of
this approach in the literature is to study the working years of
life lost, calculated over the age range from age 15 or 20 to 65
years (3,4,6,7).
YPLL Rates and Age Adjustment

When yearly trends in YPLL are compared for dynamic populations
or for substantially different populations, it may be helpful to
calculate YPLL rates per 1,000 persons in the age range. Use of
the YPLL rate adjusts the total and cause-specific YPLL for
differences in total population. For example, although the total
YPLL increased 0.4% from 1983 to 1984, the rate of YPLL per 1,000
persons decreased by 0.4% (15). Similarly, if two population
groups have different age structures, it is preferable to compare
standardized or age-adjusted YPLL rates. This rate is derived by
multiplying the age-specific death rates by a reference
population, either directly adjusting one group to the other or
adjusting both groups to an external standard. As an example,
when one compares rates of YPLL for whites with those for
American Indians and Alaskan Natives, it may be more accurate to
adjust the rates for age because of the marked difference in the
age structure of the comparison groups (16).
TRENDS IN YPLL AND YPLL RATES, 1979-1984

Premature mortality in the United States, as measured by YPLL,
decreased in the 6-year period 1979-1984 (Figure 2). The total
years of potential life lost before age 65 from all causes
decreased from 13.1 million YPLL in 1979 to 11.8 million in 1984,
a difference of 10.4%. Over 40% of this change in the total YPLL
is due to a decrease in premature mortality attributable to
unintentional injuries.

YPLL due to 10 of the 12 leading causes decreased during this
time frame (Table 4). The largest proportionate decreases were
for chronic liver disease and cirrhosis (down 22.3%),
unintentional injuries (down 19.2%), and pneumonia and influenza
(down 14.7%). In addition, a 13.1% decrease occurred in infant
deaths associated with premature birth, that is, deaths coded
with the ICD-9 rubric 765 or 769--respiratory distress syndrome
and disorders associated with short gestation and unspecified low
birth weight. Only YPLL from chronic obstructive pulmonary
disease and allied conditions (up 20.6%) and diabetes mellitus
(up 7.2%) increased.

The rate of YPLL per 1,000 persons less than 65 years of age
for all causes of death decreased by 12.8% from 1979 to 1984.
The population in the age range increased 5.5 million persons,
augmenting the decrease in the total YPLL. YPLL rates also
decreased for these same 10 leading causes of premature mortality
(Figure 3).
VARIATIONS IN THE PATTERN OF YPLL

In addition to the programmatic implications of year-to-year
changes in the total and cause-specific rates of YPLL, there may
be marked differences in the rankings of the causes of YPLL among
population subgroups. These differences can indicate populations
with an increased risk of premature mortality (e.g., males
compared with females) or identify individual causes of mortality
of particular importance in certain of these groups, such as
homicide among young black males. Interventions designed to
alter this risk could then be targeted towards groups at highest
risk, thereby increasing the effectiveness of those
interventions. In this section, we examine differences in YPLL
by race and sex and discuss its potential uses at the state and
local levels.
Racial Variations in YPLL

Rates of premature mortality differ considerably among racial
groups in the United States. During 1982, blacks had a YPLL rate
from all causes of 99.2/1,000 population, a rate nearly twice
that of whites (53.6/1,000 population). (Persons of other races
are excluded from this consideration because they constitute a
smaller and much more heterogeneous group that is not directly
comparable to the other populations.) Clearly, blacks as a group
are at increased risk of premature death when compared with
whites.

In accordance with the racial disparity in rates of premature
mortality from all causes, blacks have higher YPLL rates than
whites for all of the causes of mortality presented in Table V of
the MMWR, with ratios ranging from 1.1 to 3.6 times the rates of
the white population (Table 5). The largest ratios, those causes
for which blacks have the highest excess premature mortality, are
sudden infant death syndrome, prematurity, and pneumonia and
influenza.

Differences in the relative ranks of the leading causes of
premature mortality can also be noted between races. For
example, suicide/homicide was the leading cause of premature
mortality for blacks in 1982 (13.6 YPLL/1,000 persons), but the
fourth leading cause for whites (5.4/1,000 persons). The rates
for unintentional injuries and malignant neoplasms, however, are
more comparable (ranking first and second, respectively, for
whites, and second and fourth for blacks).
Variations in YPLL by Sex

The rate of YPLL from all causes varies considerably for males
and females. Males had a rate of 76.6 YPLL/1,000 population in
1982, nearly twice the rate for females (41.6/1,000 population).
In addition, men had higher rates than women for all of the 12
leading causes of premature mortality, with YPLL rate ratios
ranging from 1.1 to 3.5 (Table 6). The largest excess in male
premature mortality is in intentional (suicide and homicide) and
unintentional injuries, with ratios of 3.5 and 3.1, respectively.
In contrast, the rates for malignant neoplasms and
cerebrovascular diseases have male-to-female ratios of 1.1.

Similar to the differences in racial groups, the ranking of
sex-specific YPLL rates by cause varies markedly by sex. As an
illustration, although the rates for malignant neoplasms are
similar for both sexes (9.2 YPLL/1,000 population for men and
8.5/1,000 for women), malignant neoplasms are the leading cause
of premature mortality for women but only the fourth leading
cause for men. This difference reflects the excess risk of
premature mortality for men due to heart disease and
unintentional and violent injuries.
Race- and Sex-Specific YPLL Rates

To define public health priorities further, race- and
sex-specific YPLL rates can be determined. Black males had the
highest rate of YPLL from all causes in 1982, followed by black
women and white men; white women had the lowest rate (Figure 4).
Black males had 3.5 times the risk of premature mortality of
white women, while black women and white men had a rate nearly
twice that of white women. Black men have now been clearly
identified as the group most at risk of premature death and,
consequently, most in need of interventions to lower this risk.

An even more striking difference can be noted in selected
cause-specific YPLL rates (Table 7). Intentional injuries,
particularly homicide, are identified as predominantly a
condition affecting black males, with white males having the
second highest rate. In contrast, the pattern for malignant
neoplasms is more evenly distributed among all race/sex groups.
PUBLIC HEALTH USES OF YPLL

YPLL is only one of a number of mortality measures that have
broad public health applications. Yet this simple index of
premature mortality can complement traditional methods of
quantitating mortality, such as crude or age-adjusted death
rates. The major strengths of YPLL are that it is simple to
compute and comprehend and it effectively emphasizes deaths of
younger persons, in contrast to usual mortality statistics, which
are dominated by deaths of the elderly.

Geographic variations in premature mortality can also be a
useful tool for health planning at the state or local level. A
delineation of the pattern of YPLL rates among varied populations
can provide an accurate description of the causes of premature
mortality for those persons at highest risk of premature death.
This type of analysis can be done on national data, such as
presented in this document, or on local mortality data.

State-specific rates of YPLL can be used for planning and
evaluating local public health interventions. Sex- and
race-specific YPLL rates can, within the statistical limitations
of population size, be used to target and monitor those
populations at highest risk. Calculation of YPLL at the state
level is presently being evaluated by CDC in cooperation with
interested state health departments. For example, the importance
of meningitis and unintentional injuries as causes of premature
mortality in Alaska can be readily seen by the calculation of
YPLL (CDC, unpublished data).

YPLL and YPLL rates can assist in the performance of three
basic public health functions: the establishment of research and
resource priorities, the surveillance of temporal trends in
premature mortality, and the evaluation of the effectiveness of
program interventions. Within certain limitations, YPLL can
serve these functions at the national, state, or local level.
Finally, quantifying YPLL for individual causes of mortality or
for behavioral risk factors associated with a range of mortality
consequences (e.g., tobacco or alcohol use) can provide a simple
method to target health education efforts to sections of the
general population most in need of public health interventions.

U.S. Bureau of the Census. Current population reports,
series P-25, No. 965. Estimates of the population of the
United States, by age, sex, and race: 1980 to 1984.
Washington, DC: U.S. Government Printing Office, 1985.

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